The object of the present invention is the reduction of common mode current flowing between the internal ground of an electrical circuit and the Earth ground, said circuit being supplied by an electrical network. The electrical network is notably, but not exclusively, an electrical network in which the neutral is connected directly to the Earth ground.
The electrical network delivers a multiphase, or non-multiphase, alternating voltage and this voltage is rectified for supplying an energy storage unit of the electrical circuit such as a battery.
The problem that the invention aims to resolve will be explained by referring to the following non-restrictive example. The electrical circuit is, for example, on board a vehicle and may include a system of electrical propulsion of the vehicle. The vehicle further includes a frame.
When the storage unit is recharged by the electrical network, the frame is connected to the Earth ground. Due to the presence of parasitic components or not between the electrical circuit and the frame, a common mode current may flow from the circuit to the frame and loop back via the Earth ground in the electrical network.
Such a common mode current is dangerous for a user resting their feet on the ground and leaning on the frame of the vehicle.
Accordingly, there are standards for limiting the value of common mode current permissible between the part of the electrical circuit downstream from the rectifier and the frame. European standards thus limit the maximum common mode current to 3.5 mA at a frequency of 50 Hz.
To meet these standards, it is known that an isolating transformer is provided between the part of the circuit downstream from the rectifier and the frame. Such a transformer can be expensive and its integration into an already restricted space can be difficult.
It is further known that a controllable switch component is used for rectifying the current, such as a so-called PFC component (Power Factor Corrector) and specific strategies are implemented for controlling the switches. Such strategies may lead to the switches overheating and be very complex.
In the high frequency domain, through the publication “A simplified active input EMI filter of common-mode voltage cancellation for induction motor drive” an active filter is known to reduce the common mode current at high frequencies by injecting a voltage in series into the electrical network.
Also known from US patent application 2004/0004514 is an active filter seeking to reduce the common mode current at high frequencies in the field of electromagnetic compatibility (EMC).